Endoscopic surgical instruments are often preferred over traditional open surgical devices since a smaller incision tends to reduce the post-operative recovery time and complications. Consequently, significant development has gone into a range of endoscopic surgical instruments that are suitable for precise placement of a distal end effector at a desired surgical site through a cannula of a trocar. These distal end effectors engage the tissue in a number of ways to achieve a diagnostic or therapeutic effect (e.g., endocutter, grasper, cutter, staplers, clip applier, access device, drug/gene therapy delivery device, and energy device using ultrasound, RF, laser, etc.).
Known surgical staplers include an end effector that simultaneously makes a longitudinal incision in tissue and applies lines of staples on opposing sides of the incision. The end effector includes a pair of cooperating jaw members that, if the instrument is intended for endoscopic or laparoscopic applications, are capable of passing through a cannula passageway. One of the jaw members receives a staple cartridge having at least two laterally spaced rows of staples. The other jaw member defines an anvil having staple-forming pockets aligned with the rows of staples in the cartridge. The instrument includes a plurality of reciprocating wedges which, when driven distally, pass through openings in the staple cartridge and engage drivers supporting the staples to effect the firing of the staples toward the anvil.
An example of a surgical stapler suitable for endoscopic applications is described in U.S. Pat. No. 5,465,895, which discloses an endocutter with distinct closing and firing actions. A clinician using this device is able to close the jaw members upon tissue to position the tissue prior to firing. Once the clinician has determined that the jaw members are properly gripping tissue, the clinician can then fire the surgical stapler with a single firing stroke, thereby severing and stapling the tissue. The simultaneous severing and stapling avoids complications that may arise when performing such actions sequentially with different surgical tools that respectively only sever and staple.
One specific advantage of being able to close upon tissue before firing is that the clinician is able to verify via an endoscope that the desired location for the cut has been achieved, including that a sufficient amount of tissue has been captured between opposing jaws. Otherwise, opposing jaws may be drawn too close together, especially pinching at their distal ends, and thus not effectively forming closed staples in the severed tissue. At the other extreme, an excessive amount of clamped tissue may cause binding and an incomplete firing.
Endoscopic staplers/cutters continue to increase in complexity and function with each generation. One reason for this is the quest to lower force-to-fire (FTF) to a level that all or a great majority of surgeons can handle. One known solution to lower FTF uses CO2 or electrical motors. These devices have not faired much better than traditional hand-powered devices, but for a different reason. Surgeons typically prefer to experience proportionate force distribution to that being experienced by the end effector in the forming of the staple to assure them that the cutting/stapling cycle is complete, with the upper limit within the capabilities of most surgeons (usually around 15-30 lbs). They also typically want to maintain control of deploying the staples and being able to stop at anytime if the forces felt in the handle of the device feel too great or for some other clinical reason.
To address this need, so-called “power-assist” endoscopic surgical instruments have been developed in which a supplemental power source aids in the firing of the instrument. For example, in some power-assist devices, a motor provides supplemental electrical power to the power input by the user from squeezing the firing trigger. Such devices are capable of providing loading force feedback and control to the operator to reduce the firing force required to be exerted by the operator in order to complete the cutting operation. One such power-assist device is described in U.S. patent application Ser. No. 11/343,573, filed Jan. 31, 2006 by Shelton et al., entitled “Motor-driven surgical cutting and fastening instrument with loading force feedback,” (“the '573 application”) which is incorporated herein by reference.
Another reason for the increase in complexity and function of endoscopic surgical instruments is the quest to monitor and provide increased control over instrument components. For example, sensors and control systems are now being used to implement new functionality in surgical instruments including, for example, electronic lock-outs. For example, One such lockout device is described in U.S. patent application Ser. No. 11/343,439, filed Jan. 31, 2006 by Swayze et al., entitled, “Electronic Lockouts And Surgical Instrument Including Same,” which is incorporated herein by reference.
One challenge in using electronics in any kind of surgical instrument is providing a suitable power source. Most surgical instruments are stocked in sealed, sterilized packages. Because of this, it is usually not practical to access an instrument after it is packaged to verify the status of its power source or recharge if necessary. Accordingly, the shelf-life of the instrument is limited by the time that the power source is able to reliably hold a charge. For many kinds of instruments, though, it is desirable to choose a power source with a high peak power output. A high peak power output makes a power source more suitable for driving the motors, sensors and control systems used in surgical instruments. Sources with a high peak power output, however, such as lithium ion batteries, typically do not hold a full charge for a suitably long time. Accordingly, the choice of a power source must compromise the need for high peak power with a corresponding need for a long shelf-life.